Search

The electrocaloric effect (ECE), i.e., the conversion of the electric into the thermal energy has recently become of great importance for development of a new generation of cooling technologies. Here, we explore utilization of [Pb(Mg1∕3Nb2∕3)O3]0.9[PbTiO3]0.1 (PMN-10PT) relaxor ceramics as active elements of the heat regenerator in an ECE cooling device. We show that the PMN-10PT relaxor ceramic exhibits a relatively large electrocaloric change of temperature ΔTEC > 1 K at room temperature. The experimental testing of the cooling device demonstrates the efficient regeneration and establishment of the temperature span between the hot and the cold sides of the regenerator, exceeding several times the ΔTEC within a single PMN-10PT ceramic plate.

The solid-state synthesis of undoped K0.5Na0.5NbO3 (KNN) and KNN doped with 1, 2 and 6 mol% Sr, from potassium, sodium and strontium carbonates with niobium pentoxide, was studied using thermal analysis and in situ high-temperature X-ray diffraction (HT-XRD). The thermogravimetry and the differential thermal analyses with evolved-gas analyses showed that the carbonates, which were previously reacted with the moisture in the air to form hydrogen carbonates, partly decomposed when heated to 200 °C. In the temperature interval where the reaction was observed, i.e., between 200 and 750 °C, all the samples exhibited the main mass loss in two steps. The first step starts at around 400 °C and finishes at 540 °C, and the second step has an onset at 540 °C and finishes with the end of the reaction between 630 and 675 °C, depending on the particle size distribution of the Nb2O5 precursor. According to the HT-XRD analysis, the perovskite phase is formed at 450 °C for all the samples, regardless of the Sr content. The formation of a polyniobate phase with a tetragonal tungsten bronze structure was detected by HT-XRD in the KNN with the largest amount of Sr dopant, i.e., 6 mol% of Sr, at 600 °C.

The objective of this work was to examine linear thermal expansion of virgin and poled 0.57Pb(Sc 1/2 Nb 1/2 )O 3 –0.43PbTiO 3 ceramics between 30 °C and 600 °C by contact dilatometry. The thermal expansion dL / Lo of the virgin ceramic increases with increasing temperature until approximately 260 °C. The physical and technical thermal expansion coefficients were determined. At 260 °C the physical thermal coefficient is 2.08 × 10 −6 K −1 . Between 260.0 °C and 280.0 °C an anomaly in the thermal expansion vs. temperature and an endothermic peak in the differential scanning calorimetry curves correspond to the phase transition region from tetragonal to cubic phase. At temperatures from 280 °C to 600 °C the thermal expansion dL / Lo increases again. In the derivative of the dL / Lo heating curves of the poled ceramics, additionally to the anomaly at 270 °C, also the anomaly at 160 °C is observed, which is associated with the depolarization of the material during heating.

Abstract Thermal decompositions of the precursors for chemical solution deposition of 0·7 Pb(Mg1/3Nb2/3)O3-0·3 PbTiO3 (0·7PMN-0·3PT) thin films were studied. The precursors were prepared from lead acetate or acetylacetone modified lead acetate by diol based route and dried at 100°C. Thermal decompositions of the PT, PMN and PMN-PT precursors in air occur stepwise. Between room temperature and ∼200°C, the weight loss of a few per cent is due to the evaporation of residual solvents. Organic groups decompose in the ranges 200-400°C and 400-650°C. The thermal decompositions are affected by the choice of the Pb compound and chemical composition of the sample.

The electrical and microstructural characteristics of 1 kΩ/sq. thick-film NTC thermistors (4993, EMCA Remex) fired either on LTCC (low-temperature cofired ceramic) substrates or buried within LTCC structures were evaluated. The thermistors were fired at different temperatures to study the influence of firing temperature on the electrical characteristics. The results were compared with the characteristics obtained on alumina substrates. The sheet resistivities were higher than the resistivities of thick-film thermistors on alumina substrates. The increase of the sheet resistivities was attributed to the diffusion of the glass phase from the rather glassy LTCC substrates into the NTC thermistors. This was confirmed by EDS analyses. However, the increase in the resistivity was linked to an increase of the beta factors. Therefore, the results show that the evaluated NTC thermistors on LTCC substrates can be used for temperature sensors in MCM-Cs as well as in MEMS LTCC structures. When the thermistors were buried in the LTCC substrates, the LTCC structures delaminated during firing, leading to high sheet resistivities and high noise indices. This delamination is attributed to the different sintering rates of the NTC and LTCC materials.

This paper presents the crystal structure and the phase transitions of K x Na 1− x NbO 3 (0.4 ≤ x ≤ 0.6). X-ray diffraction measurements were used to follow the change of the unit-cell parameters and the symmetry in the temperature range 100–800 K. At room temperature all the compositions exhibited a monoclinic metric of the unit cell with a small monoclinic distortion (90.32° ≤ β ≤ 90.34°). No major change of symmetry was evidenced in the investigated compositional range, which should be characteristic of the morphotropic phase-boundary region. With increasing temperature, the samples underwent first-order monoclinic–tetragonal and tetragonal–cubic transitions. Only the potassium-rich phases were rhombohedral at 100 K.

Subsolidus equilibria in the RuO2–Bi2O3–SiO2 diagram were studied with the aim of investigating possible interactions between the bismuth-ruthenate- based conductive phase and the silica-rich glasses in thick-film resistors. The tie lines are between Bi2Ru2O7 and Bi12SiO20 (gamma phase), between Bi2Ru2O7 and Bi4Si3O12, and between RuO2 and Bi4Si3O12. This indicates that the bismuth ruthenate is not stable in the presence of the silica-rich glass phase.

Piezoelectric thick films based on Pb(Zr,Ti)O 3 (PZT) were prepared on two types of LTCC tapes (Du Pont 951 and Electro Science Labs. 41020) and on relatively inert alumina substrates. The results obtained with the alumina were used as a reference. The microstructures of the cross-sections of the resistors were investigated using scanning electron microscopy (SEM) and energy-dispersive X-ray (EDS) analysis. The dielectric permittivities, dielectric losses, remanent polarisation, coercive field and piezoelectric constant d 33 were measured. The dielectric and piezoelectric characteristics of the PZT fired on the LTCC substrates deteriorated in comparison to the samples on alumina, due to interactions between the LTCC substrate and the PZT layer. Lower dielectric constants, remanent polarisations and piezoelectric constants indicate the formation of phases with a low permittivity. This was attributed to the diffusion of SiO 2 from the LTCC into the active PZT layer and to the diffusion of PbO from the PZT layer into the LTCC substrate. The diffusion was confirmed by the SEM and EDS analysis.

Lead zirconate titanate (PZT) is a piezoelectric material that can sense or respond to mechanical deformations and can be used in ceramic electro-mechanical systems (C-MEMS). The microstructural, electrical, and piezoelectric characteristics of thick PZT films on low-temperature cofired ceramics (LTCC) and alumina substrates were studied. The PZT composition was prepared with low-melting-point additives in order to decrease the sintering temperature and to be compatible with thick-film technology. The integration of the PZT thick-film materials on ceramic substrates could lead to degradation of the PZT's characteristics due to the interactions between an active PZT layer and a substrate, particularly with glassy LTCC material. To minimize the interactions with LTCC substrates, an intermediate PZT barrier layer was integrated. The value of the piezoelectric coefficient d33 was found to be up to 120 pC/N on an alumina substrate and approximately 50 on an LTCC substrate. Based on these results, a cantilever-type actuator was designed and fabricated on alumina substrates. Under an applied voltage of 200 V, the maximum tip deflection was about 5 μm.

PurposeAims to evaluate different thick‐film materials for use in strain sensors and temperature sensors on low‐temperature co‐fired ceramic (LTCC) substrates.Design/methodology/approachLTCC materials are sintered at the low temperatures typically used for thick‐film processing, i.e. around 850°C, The thick‐film resistor materials for use as strain and temperature sensors on LTCC tapes are studied. Thick‐film piezo‐resistors in the form of strain‐gauges are realised with 10 kΩ/sq. 2041 (Du Pont)and 3414‐B (ESL), resistor materials; thick‐film temperature‐dependent resistors were made from PTC 5093 (Du Pont), and NTC‐4993 (EMCA Remex) resistor materials.FindingsThe X‐ray spectra of the 2041 and 3414‐Bb low TCR resistors after drying at 150°C and after firing display more or less the same peaks. The electrical characteristics of 2041 resistors fired on alumina and LTCC substrates are similar indicating that the resistors are compatible with the LTCC material. After firing on LTCC substrates the sheet resistivities and TCRs of the 3414‐B resistors increased. Also, there is a significant increase in the GFs from 13 to over 25.Originality/valueInvestigates the compatibility of thick‐film materials and the characteristics of the force and temperature sensors.

PZT thick films (PbZr 0.53 Ti 0.47 O 3 with the addition of 6% PbO and 2% Pb 5 Ge 3 O 11 ) with a low sintering temperature were printed and fired on LTCC substrates (951, Du Pont), covered with an alumina barrier layer. The electrical characteristics (remanent polarisation, coercive field, dielectric constant and dielectric loss) of these PZT thick films, together with sets prepared on “unprotected” LTCC substrates and on alumina substrates were compared. Whereas the electrical characteristics of the films on LTCC substrates deteriorated significantly due to interactions between the LTCC substrates and the PZT layers the values obtained for the LTCC/alumina barrier structures were comparable with those on ceramic alumina substrates.

The electrical and microstructural characteristics of 1 kΩ/sq. thick-film thermistors with high positive temperature coefficients of resistivity, i.e. PTC 5093 (Du Pont) fired either on “green” LTCC (low temperature cofired ceramics) substrates or buried within LTCC structures, were evaluated. The active phase (ruthenium oxide) in the PTC thermistors is not present in the dried films but is formed during firing due to the decomposition of the ruthenate phase. Because of interactions between a glassy LTCC material and thermistors electrical characteristic, i.e. sheet resistivities and noise indices of thermistors fired on the surface LTCC substrates, changed from values obtained on alumina substrates. The differences in the measured electrical parameters were attributed to the interactions between the thermistor layers and the glassy LTCC substrates. The inter-diffusion of oxides, mainly PbO and Al 2 O 3 , was confirmed by microanalysis. In the case of buried thermistors, presumably due to the incompatibility of both materials, the structure de-laminated during firing. Cracks between the buried PTC films and the LTCC substrates as well as cracks in PTC films resulted in high sheet resistivities and high noise indices.

The electrical and microstructural characteristics of 1 kΩ/sq. thick-film thermistors with high positive or negative temperature coefficients of resistivity, i.e., PTC 5093 (Du Pont) and NTC 4993 (EMCA Remex), fired on alumina or co-fired on “green” low-temperature co-fired ceramic (LTCC) substrates, are compared. The active phase in both materials (the ruthenium oxide and the semiconducting spinel in the PTC and NTC thermistors, respectively) is not present in the dried films but is formed during firing. The differences in the measured electrical parameters (sheet resistivities, temperature dependence of resistivities and noise) of the thermistors, fired on alumina or on LTCC were attributed to the interactions between the thermistor layers and the glassy LTCC substrates. The inter-diffusion of oxides, mainly PbO and SiO 2 , was confirmed by microanalysis.

The characteristics of 10 kohm/sq. thick-film resistors (2041, Du Pont and 2341-B, ESL) fired on tetragonal ZrO 2, low-temperature cofired ceramic (LTCC) and dielectric-on-steel substrates were investigated with the aim of determining the compatibility of these resistor materials, which were developed for firing on Al 2O3, with other substrates. Possible interactions between the thick-film resistors and the substrates were investigated. Sheet resistivities, temperature coefficients of resistivity, noise indices and gauge factors (GFs) were measured. The results indicate that the 2041 and 3414-B thick-film resistors could be used on the evaluated substrates if an allowance is made for the increased temperature coefficient of resistivities (TCRs) of both resistor materials on the zirconia substrates and for the increased sheet resistivities and TCRs of the 3414-B resistors on the LTCC substrates. © 2003 Elsevier B.V. All rights reserved.

The objective of this work was to examine linear thermal expansion of K0.5Na0.5NbO3 ceramics between room temperature and 790°C by contact dilatometry. The material was single phase with 95.5% relative density and with a uniform microstructure. Three distinct regions of thermal expansion could be discerned, corresponding to the three phases of K0.5Na0.5NbO3: monoclinic (assuming a single perovskite unit cell), tetragonal, and cubic, separated by discontinuities as typical for the first-order phase transitions. The linear coefficient of thermal expansion between 30° and 195°C is 2.96 × 10−6 K−1, between 208° and 364°C is 4.35 × 10−6 K−1, and between 434° and 790°C is 7.52 × 10−6 K−1.

Liquid precursors of (K(0.5)Na(0.5))NbO(3) thin-films were prepared from alkali acetates and niobium ethoxide in 2-methoxyethanol solvent either in a stoichiometric ratio or with 5 or 10 mole % of potassium or sodium acetate excess. Fourier-transform infrared (FTIR) spectroscopy of the dried precursors confirmed the presence of acetate and hydroxyl groups. Thermal decompositions of the as-dried precursors in air occurred gradually. Between room temperature and ~200 °C, the weight loss of a few per cent was due to the evaporation of residual solvents. The major mass loss was due to thermal oxidation of organic group with the major exothermic events at about 250 °C and 450 °C, almost 200 °C below the onset of the chemical decomposition of alkali acetates, indicating that a heterometallic complex was formed in solution, in agreement with FTIR analysis. Both the amount and to a lesser extent the choice of alkali-acetate excess influenced the thermal decomposition of the organic groups predominantly in the temperature interval between ~200 °C and ~400 °C.

Piezoelectric thick films based on Pb(Zr, Ti)O 3 (PZT) were prepared on LTCC substrates and on relatively inert alumina substrates. The results obtained with the alumina were used as a reference. The microstructures of the cross-sections of the PZT layers were investigated using scanning electron microscopy (SEM) and energy-dispersive X-ray (EDS) analysis. The dielectric permittivities, dielectric losses, remanent polarisations, coercitive fields and piezoelectric constants d 33 were measured. The dielectric and piezo electric characteristics of the PZT fired on the LTCC substrate deteriorated, as compared with samples on alumina, due to interactions between the LTCC substratse and the PZT layers. This was attributed to the diffusion of the glassy phasee from the LTCC into the active PZT layer and to the diffusion of the PbO from PZT layer into the LTCC substrates.

This paper presents manufacturing process of laser-shaped thick-film resistors as well as their chosen electrical, geometrical, microstructural and stability properties. Test structures were based on commercially available conductive and resistive pastes deposited on Al 2 O 3 substrates. Resistors made in standard screen printing process after firing were patterned using laser beam in order to minimize their planar dimensions to tenths of millimeter and below. Prepared samples were subjected to number of electrical tests and some characteristic parameters like temperature coefficient of resistance (TCR) were calculated based on these measurements. Test samples were also exposed to long-term thermal ageing. Moreover the laser profilometer was used for three-dimensional characterization of components. Scanning electron microscope (SEM) was used for the microstructural analysis and the EDS (Energy Dispersive X-ray Spectroscopy) of samples is given.

This paper presents the crystal structure and the phase transitions of K x Na 1− x NbO 3 (0.4 ≤ x ≤ 0.6). X-ray diffraction measurements were used to follow the change of the unit-cell parameters and the symmetry in the temperature range 100–800 K. At room temperature all the compositions exhibited a monoclinic metric of the unit cell with a small monoclinic distortion (90.32° ≤ β ≤ 90.34°). No major change of symmetry was evidenced in the investigated compositional range, which should be characteristic of the morphotropic phase-boundary region. With increasing temperature, the samples underwent first-order monoclinic–tetragonal and tetragonal–cubic transitions. Only the potassium-rich phases were rhombohedral at 100 K.

Modern advanced 3D microelectronic packages are in many cases made as multilayer ceramic modules with integrated electronic components and sub-circuits. The Low Temperature Co-Fired Ceramics (LTCC) technology is considered as one of more advanced technologies for fabrication of these structures. The increasing versatility of LTCC technology applications is a consequence of such attractive features of this technology as possibility of creation of three-dimensional structures as many of applications demand possibility of structuring of channels, cavities and reaction chambers, membranes and free-standing beams within LTCC ceramics. To obtain these buried structures without delamination and/or sagging during lamination processes (compressing of green LTCC foils at around 70°C) so called sacrificial layers are often used. During lamination sacrificial layers (screen printed thick film pastes or tapes) support buried cavities. During firing layers must burn out before LTCC tapes are densely sintered to enable the diffusion of air into structures. Six different carbon based materials (four pastes and two tapes) were evaluated. The thermo gravimetrical analysis (TGA) was used to determine the optimised burn-out temperatures and times. LTCC test structures were designed to evaluate the “quality” of buried cavities with different sacrificial materials and with different processing parameters.

For temperature sensors in MEMS (the ceramic micro electro-mechanical systems) thick-film temperature-dependent resistors PTC-5093 (Du Pont) and NTC-4993 (Ferro) resistor materials were evaluated. Thick-film piezo-resistors for strain-gauges were realised with Du Pont 2041 (low noise and very stable resistors) and ESL 341-B (high gauge factor) 10 kohm/sq. resistor materials. The PZT paste was prepared from a pre-reacted PZT powder with the composition near the morphotropic phase boundary (Zr/Ti 53/47). Thick-film PTC and NTC thermistors, ldquonormalrdquo low TCR resistors and PTZ piezoelectric pastes were printed and fired on Heraeus HL-2000 LTCC zero shrink substrates. Results obtained on relatively inert alumina substrates were used for the comparison. In most cases the required characteristics of thick film materials on LTCC substrates were inferior to those obtained on relatively inert alumina substrates. This is attributed to the inter-diffusion of oxides, mainly SiO2, from the rather glassy LTCC substrates into active layers and presumably also to the diffusion of some from oxides from thick fil layers into LTCC substrates.

Different piezoelectric materials can be used in micro-electro-mechanical systems (MEMS) for transducers i.e. actuators and sensors of mechanical quantities. Lead zirconate titanates (PZTs) are the most common ceramic materials used as piezoelectric transducers. The ceramic MEMS are made by LTCC (low temperature cofired ceramic) and thick-film technology. They have been extensively used due to their superior piezoelectric properties. The use of thick-film PZT materials on LTCC substrate is not a trivial task due to the interaction between the printed PZT layers and the LTCC substrates during firing. The microstructural, electrical and piezoelectric characteristics of the thick PZT films on relatively inert alumina substrates and on LTCC tapes were studied. To minimise the possible interactions between glassy LTCC substrates and active PZT films for some samples the intermediate barrier layers were used. To characterise the thick PZT films on ceramic substrate the dielectric permittivities (epsiv), dielectric losses (tgdelta), and piezoelectric coefficients (d33) were measured. The thick-film piezoelectric resonant pressure sensor on LTCC structure was designed and samples were fabricated (Figure 2). The thick-film PZT actuator on the ceramic diaphragm induces the vibration of the diaphragm at its resonant frequency. The applied pressure bends the diaphragm and generates additional stress, which shifts the resonant frequency. This is used as the output signal of the piezoelectric resonant pressure sensor. The resonant frequencies are shifted around 26 kHz. The calculated sensitivities are 2.5 Hz/kPa.

The electrical and microstructural characteristics of thick-film resistors fired at different temperatures and ldquoover-firedrdquo to reach an equilibrium between the glass and the conductive phases was presented. Two cases are described: resistors with a conductive phase included in the resistor paste (the majority of thick-film resistors) and resistors where the required characteristics depend on a conductive phase that forms during firing.

The aim of the work was to gain some insight into the development of the thick-film NTC thermistor's electrical characteristics, i.e,. sheet resistivity, beta factor and noise, and microstructural characteristics, during the firing process. 1 kohm/sq. thick-film NTC thermistors were fired at different temperatures. Thermistors were fired at temperatures from 500degC to 950degC, and also for a relatively long time (3 hours) at 950degC to allow reactions to reach or at least to come close to equilibrium. The dried thermistors and the thermistors fired at different temperatures were examined by XRD, SEM, and EDS microanalysis. The semiconductive spinel phase is not present in the dried thermistors but is formed during firing. Higher firing temperatures increased beta factors and significantly increased sheet resistivities. However, the noise indices were relatively low, regardless of the firing conditions. The high sheet resisitivities of samples fired for 3 hours at 950degC are presumably due to partial substitution of the B site ions with Al3+ ions in the spinel structures.

The electrical and microstructural characteristics of NTC thick-film resistors, fired either on alumina or cofired on "green" LTCC substrates are compared. The NTC resistors, fired on LTCC (as compared to resistors on alumina substrates), have higher sheet resistivities, higher beta factors, and also significantly higher noise indices. SEM and EDX analysis indicated the interaction between NTC and LTCC materials, mainly the diffusion of the glass phase from the LTCC substrate into the NTC resistor.

The development of the conductive phase in some thick-film resistors with both low and with high temperature coefficients of resistivity was studied using X-ray diffraction analysis and electron microscopy. After long-term high-temperature firing the conductive phase in thick-film resistors based on RuO2 remains unchanged, while the ruthenates decompose. This is presumably due to interactions of the ruthenate with the silica-rich glass phase in the resistors. The reaction kinetics is faster for higher concentrations of SiO2

Stoichiometric K0.5Na0.5NbO3 solid solution(KNN) was prepared by solid-state synthesis from alkaline carbonates and niobium oxide. Thermal decomposition of the powder mixture occurs upon heating to 700 °C followed by crystallization of the perovskite phase. After sintering at 1100 °C, 2h the stoichiometric KNN reaches 94 % of theoretical density. Dielectric constant of stoichiometric KNN is 620, and the losses 0.03.

International audience; Piezoelectric nanogenerators are attracting substantial attention due to the environmental constraints and ecological considerations of energy harvesting. However, the Achilles' heel of the majority of these nanogenerators is the presence of toxic compounds or the requirement of a poling process to promote higher piezoelectric effect. Here, a self-poled and bio-flexible piezoelectric nanogenerator (BF-PNG) is designed, based on lead-free biocompatible Ba0.85Ca0.15Zr0.10Ti0.90O3 nanoparticles that are functionalized with polydopamine and embedded in the polylactic acid biodegradable polymer. The BF-PNG can generate open-circuit voltage and short-circuit current of 14.4 V and 0.55 µA, respectively, under gentle finger tapping. Furthermore, it demonstrates an outstanding high mechanical robustness, stable and durable output even after one year. It achieves a maximum power density of about 7.54 mW/cm3 at a low resistive load of 3.5 MΩ. The feasibility of the BF-PNG by trigging commercial electronics such as charging capacitors and lighting a LED is verified, and the BF-PNG can drive a 1 µF capacitor to store the energy of 3.92 µJ within 115 s under gentle finger tapping. This research demonstrates that a lead-free piezoceramic in combination with a biodegradable piezopolymer can lead to a design of bio-flexible piezoelectric nanogenerators with outstanding performances and in particular useful in self-powered medical devices.